5.2 Specialised Exchange Surfaces Flashcards
What are specialised exchange surfaces?
The parts of an organism over which they exchange substances with their environment.
What is the job of the lungs?
To transfer oxygen to the blood and to remove waste carbon dioxide from it. To do this, the lungs contain millions of little air sacs called alveoli where gas exchange takes place.
What are the alveoli surrounded by?
A network of tiny blood vessels called capillaries.
How are alveoli specialised to maximise the rate of diffusion? (4)
They have:
- An enormous surface area (about 75 meters in humans).
- A moist lining for dissolving gases.
- Very thin walls (consisting of cells with partially permeable cell membranes).
- A good blood supply.
What 2 specialised exchange surfaces do plants have?
- Root hair cells: to help them absorb water and mineral ions from the soil
- Leaves: to help them absorb carbon dioxide
Where is digestive food absorbed?
Small intestine.
What is the inside of the small intestine covered in?
Millions and millions of tiny little projections called villi.
What do villi do?
Villi increase the surface area in a big way so that digested food is quickly absorbed into the blood by active transport and diffusion. For example:
- When there’s a higher concentration of glucose in the intestine, it diffuses naturally into the blood.
- When there’s a lower concentration of glucose in the intestine, it is actively transported into the blood. This allows glucose to be taken into the blood, despite the fact that the concentration gradient is the wrong way.
How are villi specialised to maximise the rate of diffusion and active transport of glucose? (3)
- Villi have a single layer of surface cells to assist quick absorption.
- They have partially permeable cell membranes, which regulate the movement of substances across them.
- Villi also have a very good blood supply to assist quick absorption.
How is water absorbed into the blood?
From the large intestine by osmosis.
What features do all specialised exchange surfaces have in common? (3)
- Large surface area: lots of molecules can diffuse across at the same time. Overall, the rate of diffusion is higher.
- The exchange surfaces are usually very thin: this means that there’s only a short distance for substances to diffuse across. This is often referred to as a “short diffusion distance”. It means that diffusion can take place more quickly.
- The exchange surfaces are permeable to the substances that they need to exchange: surfaces allow substances to diffuse across, rather than blocking them.
How does a good blood supply help villi to carry out their role?
A good blood supply helps to maintain a concentration gradient. Having a good supply of blood to your villi means that as soon as some of the glucose is absorbed into the blood, that blood will quickly be taken away and replaced with blood that doesn’t yet have lots of glucose. This helps to maintain a concentration gradient between the lumen of the intestines and the blood stream, so that more glucose can continue to diffuse down this concentration gradient into the blood.
What does a good supply of the external medium do for specialised exchange systems?
It helps maintain the concentration gradient.
State and explain 5 features that exchange surfaces in animals have (5)
- Large surface area: lots of molecules can diffuse across at the same time.
- Surfaces are very thin: substances only have to diffuse a short distance.
- Surfaces are permeable: substances are able to pass through the surface.
- Good supply of blood (‘internal medium’): maintains a strong concentration gradient as blood is constantly replaced.
- Good supply of external medium: maintains a strong concentration gradient as the air or food etc is constantly replaced.
Where are alveoli found?
Lungs
